Multi-gate device and related methods

ABSTRACT

A method of fabricating a semiconductor device includes providing a dummy structure having a plurality of channel layers, an inner spacer disposed between adjacent channels of the plurality of channel layers and at a lateral end of the channel layers, and a gate structure including a gate dielectric layer and a metal layer interposing the plurality of channel layers. The dummy structure is disposed at an active edge adjacent to an active region. A metal gate etching process is performed to remove the metal layer from the gate structure while the gate dielectric layer remains disposed at a channel layer-inner spacer interface. After performing the metal gate etching process, a dry etching process is performed to form a cut region along the active edge. The gate dielectric layer disposed at the channel layer-inner spacer interface prevents the dry etching process from damaging a source/drain feature within the adjacent active region.

BACKGROUND

The electronics industry has experienced an ever-increasing demand forsmaller and faster electronic devices which are simultaneously able tosupport a greater number of increasingly complex and sophisticatedfunctions. Accordingly, there is a continuing trend in the semiconductorindustry to manufacture low-cost, high-performance, and low-powerintegrated circuits (ICs). Thus far these goals have been achieved inlarge part by scaling down semiconductor IC dimensions (e.g., minimumfeature size) and thereby improving production efficiency and loweringassociated costs. However, such scaling has also introduced increasedcomplexity to the semiconductor manufacturing process. Thus, therealization of continued advances in semiconductor ICs and devices callsfor similar advances in semiconductor manufacturing processes andtechnology.

Recently, multi-gate devices have been introduced in an effort toimprove gate control by increasing gate-channel coupling, reduceOFF-state current, and reduce short-channel effects (SCEs). One suchmulti-gate device that has been introduced is the fin field-effecttransistor (FinFET). The FinFET gets its name from the fin-likestructure which extends from a substrate on which it is formed, andwhich is used to form the FET channel. Another multi-gate device,introduced in part to address performance challenges associated withFinFETs, is the gate-all-around (GAA) transistor. GAA devices get theirname from the gate structure which extends completely around thechannel, providing better electrostatic control than FinFETs. FinFETsand GAA devices are compatible with conventional complementarymetal-oxide-semiconductor (CMOS) processes and their three-dimensionalstructure allows them to be aggressively scaled while maintaining gatecontrol and mitigating SCEs.

To continue to provide the desired scaling and increased density formulti-gate devices in advanced technology nodes, continued reduction ofthe contacted poly pitch (CPP) (or “gate pitch”) is necessary. In atleast some existing implementations, a continuous poly on diffusion edge(CPODE) process has been used to scale the CPP. By way of example, aCPODE process may be used to provide isolation between neighboringactive regions (e.g., device regions including source, drain, and gatestructures). However, in some cases, source/drain epitaxial layersdisposed next to a CPODE region may be damaged during a CPODE etchingprocess, thereby compromising device performance and reliability. Thus,existing techniques have not proved entirely satisfactory in allrespects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a simplified top-down layout view of a multi-gatedevice, according to one or more aspects of the present disclosure;

FIG. 2 is a flow chart of a method of fabricating a multi-gate deviceaccording to one or more aspects of the present disclosure;

FIGS. 3A, 4A, 5A, 6A, 7A, 8A, 9A, and 10A provide cross-sectional viewsof an embodiment of a semiconductor device 300 along a planesubstantially parallel to a plane defined by section XX′ of FIG. 1,according to various stages of the method of FIG. 2;

FIGS. 3B, 4B, 5B, 6B, 7B, 8B, 9B, and 10B provide cross-sectional viewsof an embodiment of the semiconductor device 300 along a planesubstantially parallel to a plane defined by section YY′ of FIG. 1,according to various stages of the method of FIG. 2; and

FIGS. 9C, 9D, 9E, and 9F provide enlarged views of a portion of thesemiconductor device 300, corresponding to different spacer layerthicknesses, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

It is also noted that the present disclosure presents embodiments in theform of multi-gate transistors. Multi-gate transistors include thosetransistors whose gate structures are formed on at least two-sides of achannel region. These multi-gate devices may include a P-typemetal-oxide-semiconductor device or an N-type metal-oxide-semiconductormulti-gate device. Specific examples may be presented and referred toherein as FINFET, on account of their fin-like structure. Also presentedherein are embodiments of a type of multi-gate transistor referred to asa gate-all-around (GAA) device. A GAA device includes any device thathas its gate structure, or portion thereof, formed on 4-sides of achannel region (e.g., surrounding a portion of a channel region).Devices presented herein also include embodiments that have channelregions disposed in nanosheet channel(s), nanowire channel(s),bar-shaped channel(s), and/or other suitable channel configurations.Presented herein are embodiments of devices that may have one or morechannel regions (e.g., nanowires/nanosheets) associated with a single,contiguous gate structure. However, one of ordinary skill wouldrecognize that the teaching can apply to a single channel (e.g., singlenanowire/nanosheet) or any number of channels. One of ordinary skill mayrecognize other examples of semiconductor devices that may benefit fromaspects of the present disclosure.

Continuing to provide the desired scaling and increased density formulti-gate devices in advanced technology nodes calls for scaling of thecontacted poly pitch (CPP) (or “gate pitch”). In at least some existingimplementations, a continuous poly on diffusion edge (CPODE) process hasbeen used to scale the CPP. For purposes of this disclosure, a“diffusion edge” may be equivalently referred to as an active edge,where for example an active edge abuts adjacent active regions. Further,an active region includes a region where transistor structures areformed (e.g., including source, drain, and gate/channel structures). Insome examples, active regions may be disposed between insulatingregions. The CPODE process may provide an isolation region betweenneighboring active regions, and thus neighboring transistors, byperforming a dry etching process along an active edge (e.g., at aboundary of adjacent active regions) to form a cut region and fillingthe cut region with a dielectric, such as silicon nitride (SiN).

Before the CPODE process, the active edge may include a dummy GAAstructure having a gate stack and a plurality of channels (e.g.,nanowire/nanosheet channels). The plurality of channels may each includea chemical oxide layer formed thereon, and high-K dielectric/metal gatelayers may be formed over the chemical oxide layer and between adjacentchannels of the plurality of channels. In addition, inner spacers may bedisposed between adjacent channels at lateral ends of the plurality ofchannels. In various examples, source/drain epitaxial (epi) layers ofadjacent active regions are disposed on either side of the dummy GAAstructure (formed at the active edge), such that the adjacentsource/drain epi layers are in contact with the inner spacers andplurality of channels of the dummy GAA structure. Just prior to theCPODE etching process, a metal gate etching process may be performed toremove the metal gate layer from the dummy GAA structure.

However, in at least some existing implementations, the metal gateetching process may also remove the high-K dielectric of the dummy GAAstructure. Thus, after the metal gate etching process, the dummy GAAstructure includes the plurality of channels with the chemical oxidelayer formed thereon and the inner spacers disposed between adjacentchannels. In particular, the dummy GAA structure has weak spots betweenthe nanowire/nanosheet channels and the inner spacers, where only a thin(e.g., ˜1 nm) portion of the chemical oxide layer remains disposed nextto the source/drain epi layers of the adjacent active regions. As aresult, during the subsequent CPODE dry etching process to form the cutregion along the active edge, the adjacent source/drain epi layers maybe damaged in the region of these weak spots, where only the thin (e.g.,˜1 nm) portion of the chemical oxide layer remains to resist the CPODEdry etching process and protect the adjacent source/drain epi layers. Asa result, device performance and reliability of a transistor formed inthe adjacent active region, using the damaged source/drain epitaxiallayer, will be degraded. Thus, existing techniques have not provedentirely satisfactory in all respects.

Embodiments of the present disclosure offer advantages over the existingart, though it is understood that other embodiments may offer differentadvantages, not all advantages are necessarily discussed herein, and noparticular advantage is required for all embodiments. For example,embodiments discussed herein include structures and related methods forperforming a CPODE process without damaging source/drain epi layers ofactive regions adjacent to an active edge, as well as relatedstructures. In various embodiments, a dummy GAA structure may be formedat an active edge (e.g., at a boundary of adjacent active regions), asdescribed above, with source/drain epi layers of adjacent active regionsdisposed on either side of the dummy GAA structure. In some embodiments,and prior to the CPODE etching process, a metal gate etching process maybe performed to remove the metal gate layer from the dummy GAAstructure. However, in contrast to at least some existingimplementations, the metal gate etching process does not remove thehigh-K dielectric of the dummy GAA structure. Stated another way, themetal gate etching process selectively removes the metal gate layerwithout removing the high-K dielectric. By way of example, the selectivemetal gate etching process includes a wet etching process. In someembodiments, the selective wet etching process may include a combinationof ammonium hydroxide (NH₄OH), hydrogen peroxide (H₂O₂), and water(H₂O). Thus, in various embodiments and after the metal gate etchingprocess, regions of the dummy GAA structure between thenanowire/nanosheet channels and the inner spacers include both theunremoved high-K dielectric and the thin (e.g., ˜1 nm) portion of thechemical oxide layer disposed next to the source/drain epi layers of theadjacent active regions. The unremoved high-K dielectric thus providesanother layer, in addition to the chemical oxide layer, to resist theCPODE dry etching process and effectively mitigate weak spots, presentin at least some conventional processes, as noted above. As a result, insome embodiments and during the subsequent CPODE dry etching process toform the cut region along the active edge, damage to the adjacentsource/drain epi layers will be effectively reduced or eliminated. Byemploying the disclosed CPODE process, a CPODE process window isenlarged and device performance and reliability of transistors formed inthe adjacent active regions will be enhanced. Other embodiments andadvantages will be evident to those skilled in the art upon reading thepresent disclosure.

For purposes of the discussion that follows, FIG. 1 provides asimplified top-down layout view of a multi-gate device 100. In variousembodiments, the multi-gate device 100 may include a FinFET device, aGAA transistor, or other type of multi-gate device. The multi-gatedevice 100 may include a plurality of fin elements 104 extending from asubstrate, a gate structure 108 disposed over and around the finelements 104, and source/drain regions 105, 107, where the source/drainregions 105, 107 are formed in, on, and/or surrounding the fins 104. Achannel region of the multi-gate device 100, which may include aplurality of semiconductor channel layers (e.g., when the multi-gatedevice 100 includes a GAA transistor), is disposed within the fins 104,underlying the gate structure 108, along a plane substantially parallelto a plane defined by section XX′ of FIG. 1. In some embodiments,sidewall spacers may also be formed on sidewalls of the gate structure108. Various other features of the multi-gate device 100 are discussedin more detail below with reference to the method of FIG. 2.

Referring to FIG. 2, illustrated therein is a method 200 of fabricationof a semiconductor device 300 (e.g., which includes a multi-gate device)using a CPODE process, in accordance with various embodiments. Themethod 200 is discussed below with reference to a GAA device having achannel region that may be referred to as a nanosheet and which mayinclude various geometries (e.g., cylindrical, bar-shaped) anddimensions. However, it will be understood that aspects of the method200, including the disclosed CPODE process, may be equally applied toother types of multi-gate devices (e.g., such as FinFETs or devicesincluding both GAA devices and FinFETs) without departing from the scopeof the present disclosure. In some embodiments, the method 200 may beused to fabricate the multi-gate device 100, described above withreference to FIG. 1. Thus, one or more aspects discussed above withreference to the multi-gate device 100 may also apply to the method 200.It is understood that the method 200 includes steps having features of acomplementary metal-oxide-semiconductor (CMOS) technology process flowand thus, are only described briefly herein. Also, additional steps maybe performed before, after, and/or during the method 200.

The method 200 is described below with reference to FIGS. 3A/3B, 4A/4B,5A/5B, 6A/6B, 7A/7B, 8A/8B, 9A/9B, and 10A/10B which illustrate thesemiconductor device 300 at various stages of fabrication according tothe method 200. FIGS. 3A, 4A, 5A, 6A, 7A, 8A, 9A, and 10A providecross-sectional views of an embodiment of the semiconductor device 300along a plane substantially parallel to a plane defined by section XX′of FIG. 1. FIGS. 3B, 4B, 5B, 6B, 7B, 8B, 9B, and 10B providecross-sectional views of an embodiment of the semiconductor device 300along a plane substantially parallel to a plane defined by section YY′of FIG. 1.

Further, the semiconductor device 300 may include various other devicesand features, such as other types of devices such as additionaltransistors, bipolar junction transistors, resistors, capacitors,inductors, diodes, fuses, static random-access memory (SRAM) and/orother logic circuits, etc., but is simplified for a better understandingof the inventive concepts of the present disclosure. In someembodiments, the semiconductor device 300 includes a plurality ofsemiconductor devices (e.g., transistors), including PFETs, NFETs, etc.,which may be interconnected. Moreover, it is noted that the processsteps of method 200, including any descriptions given with reference tothe figures are merely exemplary and are not intended to be limitingbeyond what is specifically recited in the claims that follow.

The method 200 begins at block 202 where a partially fabricatedmulti-gate device is provided. Referring to the example of FIGS. 3A and3B, in an embodiment of block 202, a device 300 includes a first activeregion 303, a second active region 305, and an active edge 307 that isdefined at a boundary of the first active region 303 and the secondactive region 305. In some embodiments, the first active region 303includes a first GAA device 309, the second active region 305 includes asecond GAA device 311, and the active edge 307 includes a dummy GAAstructure 313, as described below. In accordance with embodiments of thepresent disclosure, a CPODE process may provide an isolation regionbetween the first active region 303 and the second active region 305,and thus between the first and second GAA devices 309, 311, byperforming a dry etching process along the active edge 307 to form a cutregion and filling the cut region with a dielectric, as described inmore detail below.

Each of the first GAA device 309, the second GAA device 311, and thedummy GAA structure 313 are formed on a substrate 302 having fins 304.In some embodiments, the substrate 302 may be a semiconductor substratesuch as a silicon substrate. The substrate 302 may include variouslayers, including conductive or insulating layers formed on asemiconductor substrate. The substrate 302 may include various dopingconfigurations depending on design requirements as is known in the art.The substrate 302 may also include other semiconductors such asgermanium, silicon carbide (SiC), silicon germanium (SiGe), or diamond.Alternatively, the substrate 302 may include a compound semiconductorand/or an alloy semiconductor. Further, the substrate 302 may optionallyinclude an epi layer, may be strained for performance enhancement, mayinclude a silicon-on-insulator (SOI) structure, and/or have othersuitable enhancement features.

The fins 304 may include nanosheet channel layers 306. In someembodiments, the nanosheet channel layers 306 may include silicon (Si).However, in some embodiments, the nanosheet channel layers 306 mayinclude other materials such as germanium, a compound semiconductor suchas silicon carbide, gallium arsenide, gallium phosphide, indiumphosphide, indium arsenide, and/or indium antimonide, an alloysemiconductor such as SiGe, GaAsP, AlInAs, AlGaAs, InGaAs, GaInP, and/orGaInAsP, or combinations thereof. By way of example, the nanosheetchannel layers 306 may be epitaxially grown by a molecular beam epitaxy(MBE) process, a metalorganic chemical vapor deposition (MOCVD) process,and/or other suitable epitaxial growth processes.

With reference to the X and Y dimensions of the nanosheet channel layers306 from an end-view of the nanosheet channel layers 306 (e.g., FIG.3B), the X-dimension may be equal to about 5-14 nm, and the Y-dimensionmay be equal to about 5-8 nm. In some cases, the X-dimension of thenanosheet channel layers 306 is substantially the same as theY-dimension of the nanosheet channel layers 306. By way of example, thenanosheet channel layers 306 may be referred to as “nanosheets” when theX-dimension is greater than the Y-dimension. In some cases, a spacing(e.g., along the Y-direction) between adjacent nanosheet channel layers306 is equal to about 4-8 nm.

In various embodiments, each of the fins 304 includes a substrateportion 302A formed from the substrate 302 and the nanosheet channellayers 306. It is noted that while the fins 304 are illustrated asincluding three (3) nanosheet channel layers 306, this is forillustrative purposes only and is not intended to be limiting beyondwhat is specifically recited in the claims. It can be appreciated thatany number of nanosheet channel layers 306 can be formed, where forexample, the number of nanosheet channel layers 306 depends on thedesired number of channels regions for the GAA device (e.g., the device300). In some embodiments, the number of nanosheet channel layers 306 isbetween 3 and 10.

Shallow trench isolation (STI) features 317 may also be formedinterposing the fins 304. In some embodiments, the STI features 317include SiO₂, silicon nitride, silicon oxynitride, fluorine-dopedsilicate glass (FSG), a low-k dielectric, combinations thereof, and/orother suitable materials known in the art. In various examples, thedielectric layer used to form the STI features 317 may be deposited by aCVD process, a subatmospheric CVD (SACVD) process, a flowable CVDprocess, an ALD process, a PVD process, and/or other suitable process.

In various examples, each of the first GAA device 309, the second GAAdevice 311, and the dummy GAA structure 313 of the device 300 furtherincludes a gate structure, which may include a high-K/metal gate stack.In some embodiments, the gate structure may form the gate associatedwith the multi-channels provided by the nanosheet channel layers 306 inthe channel region of the first GAA device 309 and the second GAA device311. The gate structure may include an interfacial layer (IL) 308 (whichis better illustrated in FIGS. 8A/8B) and a high-K gate dielectric layer310 formed over the interfacial layer 308. In some embodiments, the gatedielectric has a total thickness of about 1-5 nm. High-K gatedielectrics, as used and described herein, include dielectric materialshaving a high dielectric constant, for example, greater than that ofthermal silicon oxide (˜3.9).

In some embodiments, the interfacial layer 308 may include a dielectricmaterial such as silicon oxide (SiO₂), HfSiO, or silicon oxynitride(SiON). The interfacial layer 308 may be formed by chemical oxidation,thermal oxidation, atomic layer deposition (ALD), chemical vapordeposition (CVD), and/or other suitable method. In some examples, theinterfacial layer 308 includes the chemical oxide layer, discussedabove. The high-K gate dielectric layer 310 may include a high-Kdielectric material such as hafnium oxide (HfO₂). Alternatively, thehigh-K gate dielectric layer 310 may include other high-K dielectricmaterials, such as TiO₂, HfZrO, Ta₂O₃, HfSiO₄, ZrO₂, ZrSiO₂, LaO, AlO,ZrO, TiO, Ta₂O₅, Y₂O₃, SrTiO₃ (STO), BaTiO₃ (BTO), BaZrO, HfZrO, HfLaO,HfSiO, LaSiO, AlSiO, HfTaO, HfTiO, (Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄,oxynitrides (SiON), combinations thereof, or other suitable material.The high-K gate dielectric layer 310 may be formed by ALD, physicalvapor deposition (PVD), CVD, oxidation, and/or other suitable methods.

The gate structure may further include a metal gate having a metal layer312 formed over the gate dielectric (e.g. over the IL 308 and the high-Kgate dielectric layer 310). The metal layer 312 may include a metal,metal alloy, or metal silicide. The metal layer 312 may include a singlelayer or alternatively a multi-layer structure, such as variouscombinations of a metal layer with a selected work function to enhancethe device performance (work function metal layer), a liner layer, awetting layer, an adhesion layer, a metal alloy or a metal silicide. Byway of example, the metal layer 312 may include Ti, Ag, Al, TiAlN, TaC,TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru, Mo, Al, WN, Cu, W, Re, Ir, Co, Ni,other suitable metal materials or a combination thereof. In variousembodiments, the metal layer 312 may be formed by ALD, PVD, CVD, e-beamevaporation, or other suitable process. Further, the metal layer 312 maybe formed separately for N-type and P-type transistors which may usedifferent metal layers. In addition, the metal layer 312 may provide anN-type or P-type work function, may serve as a transistor gateelectrode, and in at least some embodiments, the metal layer 312 mayinclude a polysilicon layer. As shown in FIG. 3A, the gate structureincludes portions that interpose each of the nanosheet channel layers306 of the fins 304, where the nanosheet channel layers 306 each providesemiconductor channel layers for the first GAA device 309 and the secondGAA device 311.

In some examples, a metal layer 329 may be formed over the metal layer312, as shown. In some embodiments, the metal layer 329 includesselectively-grown tungsten (W), although other suitable metals may alsobe used. In at least some examples, the metal layer 329 includes afluorine-free W (FFW) layer. In various examples, the metal layer 329may serve as an etch-stop layer and may also provide reduced contactresistance (e.g., to the metal layer 312).

In some embodiments, a spacer layer 315 may be formed on sidewalls of atop portion of the gate structure of each of the first GAA device 309,the second GAA device 311, and the dummy GAA structure 313. The spacerlayer 315 may be formed prior to formation of the high-K/metal gatestack of the gate structure. For example, in some cases, the spacerlayer 315 may be formed on sidewalls of a previously formed dummy(sacrificial) gate stack that is removed and replaced by thehigh-K/metal gate stack, described above, as part of a replacement gate(gate-last) process. In some cases, the spacer layer 315 may have athickness of about 2-10 nm. In various embodiments, the thickness of thespacer layer 315 may be selected to provide a desired sidewall profilefollowing a subsequent CPODE dry etching process, as discussed in moredetail below. In some examples, the spacer layer 315 may include adielectric material such as silicon oxide, silicon nitride, siliconcarbide, silicon oxynitride, SiCN, silicon oxycarbide, SiOCN, SiOHCN, alow-K material (e.g., with a dielectric constant ‘k’<7), and/orcombinations thereof. In some embodiments, the spacer layer 315 includesmultiple layers, such as main spacer layers, liner layers, and the like.

In various examples, each of the first GAA device 309, the second GAAdevice 311, and the dummy GAA structure 313 of the device 300 furtherincludes inner spacers 319. The inner spacers 319 may be disposedbetween adjacent channels of the nanosheet channel layers 306, atlateral ends of the nanosheet channel layers 306, and in contact withportions of the gate structure that interpose each of the nanosheetchannel layers 306. In some embodiments, the inner spacers 319 includeamorphous silicon. In some examples, the inner spacers 319 may includesilicon oxide, silicon nitride, silicon carbide, silicon oxynitride,SiCN, silicon oxycarbide, SiOCN, a low-K material (e.g., with adielectric constant ‘k’<7), and/or combinations thereof. In variousexamples, the inner spacers 319 may extend beneath the spacer layer 315,described above, while abutting adjacent source/drain features,described below.

In some embodiments, source/drain features 321 are formed insource/drain regions adjacent to and on either side of the gatestructure of each of the first GAA device 309 and the second GAA device311 and over the substrate portion 302A. As a result, the dummy GAAstructure 313 is disposed between a first source/drain feature 321 ofthe first GAA device 309 (in the first active region 303) and a secondsource/drain feature 321 of the second GAA device 311 (in the secondactive region 305). As shown, the source/drain features 321 of the firstGAA device 309 are in contact with the inner spacers 319 and nanosheetchannel layers 306 of the first GAA device 309, and the source/drainfeatures 321 of the second GAA device 311 are in contact with the innerspacers 319 and nanosheet channel layers 306 of the second GAA device311. Moreover, the source/drain features 321 (of the first and secondGAA devices 309, 311) disposed on either side of the dummy GAA structure313 are in contact with the inner spacers 319 and nanosheet channellayers 306 of the dummy GAA structure 313.

In various examples, the source/drain features 321 include semiconductorepi layers such as Ge, Si, GaAs, AlGaAs, SiGe, GaAsP, SiP, or othersuitable material, which may be formed by one or more epitaxialprocesses. In some embodiments, the source/drain features 321 may bein-situ doped during the epi process. For example, in some embodiments,epitaxially grown SiGe source/drain features may be doped with boron. Insome cases, epitaxially grown Si source/drain features may be doped withcarbon to form Si:C source/drain features, phosphorous to form Si:Psource/drain features, or both carbon and phosphorous to form SiCPsource/drain features. In some embodiments, the source/drain features321 are not in-situ doped, and instead an implantation process isperformed to dope the source/drain features 321. In some embodiments,formation of the source/drain features 321 may be performed in separateprocessing sequences for each of N-type and P-type source/drainfeatures.

An inter-layer dielectric (ILD) layer 323 may also be formed over thedevice 300. In some embodiments, a contact etch stop layer (CESL) 327 isformed over the device 300 prior to forming the ILD layer 323. In someexamples, the CESL 327 includes a silicon nitride layer, silicon oxidelayer, a silicon oxynitride layer, and/or other materials known in theart. The CESL 327 may be formed by plasma-enhanced chemical vapordeposition (PECVD) process and/or other suitable deposition or oxidationprocesses. In some embodiments, the ILD layer 323 includes materialssuch as tetraethylorthosilicate (TEOS) oxide, un-doped silicate glass,or doped silicon oxide such as borophosphosilicate glass (BPSG), FSG,phosphosilicate glass (PSG), boron doped silicon glass (BSG), and/orother suitable dielectric materials. The ILD layer 323 may be depositedby a PECVD process or other suitable deposition technique. In someembodiments, a hard mask layer 325 may be formed over the ILD layer 323.In some cases, the hard mask layer 325 may include SiN. In variousexamples, the ILD layer 323 and the hard mask layer 325 may bepatterned, resulting in the structure of FIG. 3A, as part of a processused to remove the previously formed dummy (sacrificial) gate stack andreplace it with the high-K/metal gate stack.

In some cases, a material layer 331 may further be formed over thedevice 300, including over the metal layer 329. In some embodiments, thematerial layer 331 includes silicon (Si). However, in some examples, thematerial layer 331 may include a dielectric material such as siliconoxide, silicon nitride, silicon carbide, silicon oxynitride,combinations thereof, or another suitable material. In addition, anitride layer 333 may be formed over the material layer 331. In someembodiments, the nitride layer 333 includes SiN. The nitride layer 333may also be used as a hard mask layer.

The method 200 then proceeds to block 204 where a cut metal gate (CMG)process is performed. With reference to FIG. 3B, in an embodiment ofblock 204 and after forming the nitride layer 333, a cut metal gateprocess is performed to isolate the metal layers 312 of adjacentstructures. By way of example, a photolithography and etch process maybe performed to etch portions of the nitride layer 333, the materiallayer 331, the metal layer 329, the metal layer 312, and the high-K gatedielectric layer 310 to form trenches 350 in cut metal gate regions 355.In some embodiments, formation of the trenches 350 exposes portions ofthe underlying STI features 317. In various examples, the trenches 350may be etched using a dry etch (e.g., reactive ion etching), a wet etch,or a combination thereof. In addition, as shown in FIG. 3B, the trenches350 may have a sidewall profile with a substantially vertical profile350A along an upper portion of the trenches 350, and a tapered profile350B along a lower portion of the trenches 350. In some embodiments,tapering the trenches 350 to form the tapered profile 350B along thelower portion of the trenches 350 may be performed to increase a spacingbetween the nanosheet channel layers 306 in adjacent active regions andthe trenches 350 (e.g., to protect the nanosheet channel layers 306 frompotential damage during the etching process and/or to improve theisolation between neighboring active regions provided by the CPODEprocess, as described in more detail below).

The method 200 then proceeds to block 206 where a refill process isperformed. With reference to FIGS. 3A/3B and 4A/4B, in an embodiment ofblock 206, a refill process is used to form a nitride layer 402 over thedevice 300, including over the nitride layer 333. The nitride layer 402is also used to fill the previously formed trenches 350 and electricallyisolate the metal layers 312 of adjacent structures. In someembodiments, the nitride layer 402 includes SiN. Alternatively, in somecases, the nitride layer 402 may include SiO₂, silicon oxynitride, FSG,a low-k dielectric, combinations thereof, and/or other suitablematerials known in the art. In various examples, the nitride layer 402may be deposited by a CVD process, an SACVD process, a flowable CVDprocess, an ALD process, a PVD process, and/or other suitable process.In some cases, after depositing the nitride layer 402, a chemicalmechanical poslishing (CMP) process may be performed to remove excessmaterial and planarize a top surface of the device 300.

The method 200 then proceeds to block 208 where a photolithography(photo) process is performed. With reference to FIGS. 4A/4B and 5A/5B,in an embodiment of block 208, a photoresist (resist) layer is deposited(e.g., using a spin-coating process) over the device 300 and patternedto form a patterned resist layer 502 that exposes a portion of thenitride layer 402. In various embodiments, the photo process used toform the patterned resist layer 502 may also include other steps such assoft baking, mask aligning, exposure, post-exposure baking, developing,rinsing, drying (e.g., spin-drying and/or hard baking), other suitablelithography processes, and/or combinations thereof. In some embodiments,the photo process of block 208 may include a CPODE photo process, wherethe patterned resist layer 502 provides an opening 504 in a CPODE region506 that exposes the portion of the nitride layer 402. In addition, theCPODE region 506 may include the active edge 307 and the dummy GAAstructure 313, discussed above with reference to FIG. 3A.

The method 200 then proceeds to block 210 where etching and resistremoval processes are performed. With reference to FIGS. 5A/5B and6A/6B, in an embodiment of block 210, an etching process is performed toremove portions of the nitride layer 402 and the nitride layer 333(e.g., in a region exposed by the opening 504 in the patterned resistlayer 502) to form an opening 604. Thus, in some examples, the etchingprocess of block 210 may be referred to as a SiN etching process, a hardmask etching process, or a SiN hard mask etching process. In variousembodiments, the opening 604 formed by the etching process may expose aportion of the material layer 331 within the CPODE region 506. In someexamples, the etching process may include a dry etching process, a wetetching process, and/or a combination thereof. After the etchingprocess, and in a further embodiment of block 210, the patterned resistlayer 502 may be removed, for example, by way of a solvent, resiststripper, ashing, or other suitable technique.

The method 200 then proceeds to block 212 where an etching process isperformed. With reference to FIGS. 6A/6B and 7A/7B, in an embodiment ofblock 212, an etching process is performed to remove portions of thematerial layer 331 (e.g., in a region exposed by the opening 604) toform an opening 704. In various embodiments, for example when thematerial layer 331 includes silicon (Si), the etching process of block212 may include a Si etching process or a Si dry etching process. Insome examples, the opening 704 formed by the etching process of block212 may expose the dummy gate GAA structure 313 within the CPODE region506. In particular, the opening 704 may expose the metal layer 329,portions of the spacer layer 315, and in some cases portions of the CESL327 within the CPODE region 506. In some examples, the etching processof block 212 may include a dry etching process, a wet etching process,and/or a combination thereof.

The method 200 then proceeds to block 214 where a metal gate etchingprocess is performed. With reference to FIGS. 7A/7B and 8A/8B, in anembodiment of block 214, the metal gate etching process includes removalof the metal layer 312 from the dummy GAA structure 313. For clarity ofthe discussion that follows, FIGS. 8A/8B include enlarged views ofportions of the device 300, as indicated by the dashed lines. In someembodiments, the metal gate etching process also includes removal of themetal layer 329 either prior to, or during, the removal of the metallayer 312. The metal gate etching process may be performed through theopening 704, resulting in an opening 804. In various embodiments,removal of one or both of the metal layers 312, 329 may include a wetetching process. By way of example, the wet etching process may includea combination of ammonium hydroxide (NH₄OH), hydrogen peroxide (H₂O₂),and water (H₂O). In accordance with embodiments of the presentdisclosure, the wet etching process of block 214 removes the metallayers 312, 329 without removing the high-K gate dielectric layer 310 ofthe dummy GAA structure 313. Stated another way, the wet etching processselectively removes the metal layers 312, 329 without removing thehigh-K gate dielectric layer 310. Thus, the wet etching process of block214 may be referred to as a selective etching process or a selective wetetching process. It is noted that the wet etching process may remove themetal layers 312 from a top portion of the dummy GAA structure 313, aswell as between adjacent channels of the nano sheet channel layers 306.

After the metal gate etching process of block 214, regions 802 of thedummy GAA structure 313 between the nanosheet channel layers 306 and theinner spacers 319 (e.g., at a top or bottom edge of the inner spacers319) include both the unremoved high-K gate dielectric layer 310 andinterfacial layer 308 disposed next to the source/drain feature 321 ofan adjacent device (e.g., the first GAA device 309 and the second GAAdevice 311) in an adjacent active region (e.g., the first active region303 and the second active region 305). In some cases, the regions 802may be referred to as a channel layer-inner spacer interface. Theunremoved high-K gate dielectric layer 310 thus provides another layer,in addition to the interfacial layer 308, to resist the CPODE dryetching process and effectively mitigate weak spots, present in at leastsome conventional processes, as previously noted. As a result, in someembodiments and during the subsequent CPODE dry etching process to formthe cut region along the active edge 307, damage to the adjacentsource/drain features 321 will be effectively reduced or eliminated. Assuch, device performance and reliability of transistors (e.g., the firstGAA device 309 and the second GAA device 311) formed in the adjacentactive regions will be enhanced.

The method 200 then proceeds to block 216 where a CPODE etching processis performed. With reference to FIGS. 8A/8B and 9A/9B, in an embodimentof block 216, the CPODE etching process etches the device 300 throughthe opening 804 within the CPODE region 506 to form a trench 904. Insome cases, the CPODE etching process includes a dry etching process.For clarity discussion, FIG. 9A includes an enlarged view of a portionsof the device 300, as indicated by the dashed lines. In someembodiments, the CPODE etching process removes portions of the nanosheetchannel layers 306, the inner spacers 319, the high-K gate dielectriclayer 310, and the interfacial layer 308 within the CPODE region 506that are not protected by (disposed directly below) the spacer layer315. As a result, the trench 904 may include nanosheet channel layerportions 306A, inner spacer portions 319A, high-K gate dielectric layerportions 310A, and interfacial layer portions 308A along sidewalls (in asidewall region) of the trench 904 and disposed between the trench 904and the adjacent source/drain feature 321. In particular, the remaininghigh-K gate dielectric layer portions 310A further illustrate thebenefit of the additional layer of protection provided by the unremovedhigh-K gate dielectric layer 310, in addition to the interfacial layer308, to resist the CPODE dry etching process and effectively mitigateweak spots, thus preventing damage to the adjacent source/drain features321. It is also noted that the CPODE etching process may, in addition toremoving substantial portions of the nanosheet channel layers 306,remove the substrate portion 302A of the dummy GAA structure 313 withinthe CPODE region 506 to form a trench 906.

As previously discussed, the thickness of the spacer layer 315 may beselected to provide a desired sidewall profile following the CPODEetching process. For example, thicker spacer layers 315 may serve toprotect greater portions of the nanosheet channel layers 306, the innerspacers 319, the high-K gate dielectric layer 310, and the interfaciallayer 308 within the CPODE region 506 that are disposed beneath thespacer layer 315, as compared to thinner spacer layers 315. For purposesof illustration, reference is made to FIGS. 9C-9F. FIG. 9C may be thesame as the enlarged portion of FIG. 9A (indicated by the dashed lines),discussed above, and FIG. 9C may correspond to a first spacer layer 315thickness ‘T1’. FIG. 9D may correspond to a second spacer layer 315thickness ‘T2’, where T2 is greater than T1. FIG. 9E may correspond to athird spacer layer 315 thickness ‘T3’, where T3 is greater than T2. FIG.9F may correspond to a fourth spacer layer 315 thickness ‘T4’, where T4is greater than T3. As shown in FIGS. 9C-9F, greater or lesser amountsof each of the nanosheet channel layers 306, the inner spacers 319, thehigh-K gate dielectric layer 310, and the interfacial layer 308 remainafter the CPODE etching process, depending on the thickness of thespacer layer 315, resulting in different amounts of resistance to theCPODE etching process for different spacer layer 315 thicknesses.Specifically, and in some embodiments, an amount of the high-K gatedielectric layer 310 that remains disposed at the channel layer-innerspacer interface corresponds to a thickness of the spacer layer 315. Insome embodiments, the spacer layer 315 thickness, and resulting sidewallprofile, may be chosen to provide more or less protection to adjacentsource/drain features 321, depending on various device and/or processparameters and specifications.

The method 200 then proceeds to block 218 where a refill process isperformed. With reference to FIGS. 9A/9B and 10A/10B, in an embodimentof block 218, a refill process is used to form a nitride layer 1002 overthe device 300 and within the trench 904 formed by the CPODE etchingprocess. The nitride layer 1002, and more generally the CPODE processdescribed herein, thus provides an isolation region between the firstactive region 303 and the second active region 305, including betweenthe first and second GAA devices 309, 311, by performing the CPODEetching process along the active edge 307 to form a cut region (thetrench 904) and filling the cut region with the nitride layer 1002. Insome embodiments, the nitride layer 1002 includes SiN. Alternatively, insome cases, the nitride layer 1002 may include SiO₂, silicon oxynitride,FSG, a low-k dielectric, combinations thereof, and/or other suitablematerials known in the art. In various examples, the nitride layer 1002may be deposited by a CVD process, an SACVD process, a flowable CVDprocess, an ALD process, a PVD process, and/or other suitable process.In some cases, after depositing the nitride layer 1002, a CMP processmay be performed to remove excess material and planarize a top surfaceof the device 300.

Generally, the semiconductor device 300 may undergo further processingto form various features and regions known in the art. For example,subsequent processing may form contact openings, contact metal, as wellas various contacts/vias/lines and multilayer interconnect features(e.g., metal layers and interlayer dielectrics) on the substrate 302,configured to connect the various features to form a functional circuitthat may include one or more multi-gate devices. In furtherance of theexample, a multilayer interconnection may include verticalinterconnects, such as vias or contacts, and horizontal interconnects,such as metal lines. The various interconnection features may employvarious conductive materials including copper, tungsten, and/orsilicide. In one example, a damascene and/or dual damascene process isused to form a copper related multilayer interconnection structure.Moreover, additional process steps may be implemented before, during,and after the method 200, and some process steps described above may bereplaced or eliminated in accordance with various embodiments of themethod 200. Further, while the method 200 has been shown and describedas including the device 300 having a GAA device, it will be understoodthat other device configurations are possible. In some embodiments, themethod 200 may be used to fabricate FinFET devices or other multi-gatedevices.

With respect to the description provided herein, disclosed arestructures and related methods for performing a CPODE process withoutdamaging source/drain epi features of active regions adjacent to anactive edge. In some embodiments, a dummy GAA structure may be formed atthe active edge, with source/drain epi features of adjacent activeregions disposed on either side of the dummy GAA structure. Prior to theCPODE etching process, a metal gate etching process is performed toremove the metal gate layer from the dummy GAA structure. In someexamples, the metal gate etching process selectively removes the metalgate layer without removing the high-K dielectric of the dummy GAAstructure. The metal gate etching process may include a wet etchcomposed of a combination of ammonium hydroxide (NH₄OH), hydrogenperoxide (H₂O₂), and water (H₂O). After the metal gate etching process,regions of the dummy GAA structure between the nanowire/nanosheetchannels and the inner spacers include both the unremoved high-Kdielectric and the interfacial layer (chemical oxide layer) disposednext to the source/drain epi features of the adjacent active regions.The unremoved high-K dielectric thus provides another layer, in additionto the interfacial, to resist the CPODE dry etching process andeffectively mitigate weak spots, present in at least some conventionalprocesses, as described above. Thus, during the CPODE dry etchingprocess, damage to the adjacent source/drain epi features will beeffectively reduced or eliminated. By employing the disclosed CPODEprocess, a CPODE process window is enlarged and device performance andreliability of transistors formed in the adjacent active regions will beenhanced. Those of skill in the art will readily appreciate that themethods and structures described herein may be applied to a variety ofother semiconductor devices to advantageously achieve similar benefitsfrom such other devices without departing from the scope of the presentdisclosure.

Thus, one of the embodiments of the present disclosure described amethod including providing a dummy structure having a plurality ofchannel layers, an inner spacer disposed between adjacent channels ofthe plurality of channel layers and at a lateral end of the channellayers, and a gate structure including a gate dielectric layer and ametal layer interposing the plurality of channel layers. In someembodiments, the dummy structure is disposed at an active edge adjacentto an active region. In some examples, the method further includesperforming a metal gate etching process to remove the metal layer fromthe gate structure while the gate dielectric layer remains disposed at achannel layer-inner spacer interface. In various embodiments, the methodfurther includes after performing the metal gate etching process,performing a dry etching process to form a cut region along the activeedge. In some embodiments, the gate dielectric layer disposed at thechannel layer-inner spacer interface prevents the dry etching processfrom damaging a source/drain feature within the adjacent active region.

In another of the embodiments, discussed is a method includingfabricating a device including a first transistor in a first activeregion, a second transistor in a second active region, and a dummytransistor at a boundary between the first and second active regions. Insome embodiments, each of the first transistor, the second transistor,and the dummy transistor include a gate dielectric layer disposed onsurfaces of adjacent channel layers and a metal gate layer disposed onthe gate dielectric layer. In some examples, the method further includesforming a material layer over each of the first transistor, the secondtransistor, and the dummy transistor and etching a portion of thematerial layer to expose the dummy transistor. In various embodiments,the method further includes after exposing the dummy transistor,removing the metal gate layer from the dummy transistor without removingthe gate dielectric layer from the dummy transistor. In some cases, themethod further includes after removing the metal gate layer from thedummy transistor, forming a first trench through the dummy transistor atthe boundary between the first and second active regions. In someexamples, at least a portion of the gate dielectric layer from the dummytransistor, disposed along a sidewall of the first trench, preventsetching of source/drain features within each of the first and secondactive regions.

In yet another of the embodiments, discussed is a semiconductor deviceincluding a transistor disposed in an active region, where thetransistor includes a source/drain feature. In some embodiments, thesemiconductor device further includes an isolation region disposed at anactive edge, the active edge defined at a boundary of the active region,where the isolation region includes a nitride-filled trench. In someexamples, the semiconductor device further includes a trench sidewallregion disposed between and in contact with each of the isolation regionand the source/drain feature, where the trench sidewall region providesseparation between the isolation region and the source/drain feature,and where the trench sidewall region includes a plurality of high-K gatedielectric layer portions.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of fabricating a semiconductor device,comprising: providing a dummy structure including a plurality of channellayers, an inner spacer disposed between adjacent channels of theplurality of channel layers and at a lateral end of the channel layers,and a gate structure including a gate dielectric layer and a metal layerinterposing the plurality of channel layers, wherein the dummy structureis disposed at an active edge adjacent to an active region; performing ametal gate etching process to remove the metal layer from the gatestructure while the gate dielectric layer remains disposed at a channellayer-inner spacer interface; and after performing the metal gateetching process, performing a dry etching process to form a cut regionalong the active edge, wherein the gate dielectric layer disposed at thechannel layer-inner spacer interface prevents the dry etching processfrom damaging a source/drain feature within the adjacent active region.2. The method of claim 1, wherein the gate dielectric layer includesboth an interfacial layer and a high-K gate dielectric layer.
 3. Themethod of claim 1, wherein performing the metal gate etching processincludes performing a wet etching process.
 4. The method of claim 3,wherein the wet etching process includes a combination of ammoniumhydroxide (NH₄OH), hydrogen peroxide (H₂O₂), and water (H₂O).
 5. Themethod of claim 1, further comprising: after performing the dry etchingprocess, performing a refill process to form a nitride layer within thecut region.
 6. The method of claim 1, wherein the gate structureincludes a spacer layer disposed on sidewalls of a top portion of thegate structure, and wherein an amount of the gate dielectric layer thatremains disposed at the channel layer-inner spacer interface correspondsto a thickness of the spacer layer.
 7. The method of claim 1, furthercomprising: prior to performing the metal gate etching process,performing a silicon (Si) dry etching process to remove a silicon layerdisposed over the gate structure.
 8. The method of claim 1, wherein thedummy structure includes a dummy gate-all-around (GAA) structure.
 9. Amethod, comprising: fabricating a device including a first transistor ina first active region, a second transistor in a second active region,and a dummy transistor at a boundary between the first and second activeregions, wherein each of the first transistor, the second transistor,and the dummy transistor include a gate dielectric layer disposed onsurfaces of adjacent channel layers and a metal gate layer disposed onthe gate dielectric layer; forming a material layer over each of thefirst transistor, the second transistor, and the dummy transistor andetching a portion of the material layer to expose the dummy transistor;after exposing the dummy transistor, removing the metal gate layer fromthe dummy transistor without removing the gate dielectric layer from thedummy transistor; and after removing the metal gate layer from the dummytransistor, forming a first trench through the dummy transistor at theboundary between the first and second active regions, wherein at least aportion of the gate dielectric layer from the dummy transistor, disposedalong a sidewall of the first trench, prevents etching of source/drainfeatures within each of the first and second active regions.
 10. Themethod of claim 9, wherein each of the first transistor, the secondtransistor, and the dummy transistor include an inner spacer disposedbetween the adjacent channel layers and at a lateral end of the adjacentchannel layers.
 11. The method of claim 10, wherein the portion of thegate dielectric layer from the dummy transistor, disposed along thesidewall of the first trench, is disposed at a channel layer-innerspacer interface.
 12. The method of claim 9, wherein the gate dielectriclayer includes an interfacial layer and a high-K gate dielectric layerdisposed over the interfacial layer.
 13. The method of claim 9, whereinthe removing the metal gate layer includes removing the metal gate layerusing a wet etching process, and wherein the wet etching processincludes a combination of ammonium hydroxide (NH₄OH), hydrogen peroxide(H₂O₂), and water (H₂O).
 14. The method of claim 9, further comprising:prior to removing the metal gate layer from the dummy transistor,performing a cut metal gate process to cut a portion of the metal gatelayer disposed between adjacent fins and form a second trench; andperforming a first refill process to form a first nitride layer withinthe second trench and electrically isolate portions of the metal gatelayer of adjacent fins.
 15. The method of claim 14, further comprising:after forming the first nitride layer within the second trench, etchinga portion of the first nitride layer and the material layer to exposethe dummy transistor.
 16. The method of claim 9, further comprising:after forming the first trench, performing a second refill process toform a second nitride layer within the first trench.
 17. The method ofclaim 9, wherein the portion of the gate dielectric layer from the dummytransistor is disposed adjacent to the first trench and beneath a gatespacer layer of the dummy transistor.
 18. A semiconductor device,comprising: a transistor disposed in an active region, wherein thetransistor includes a source/drain feature; an isolation region disposedat an active edge, the active edge defined at a boundary of the activeregion, wherein the isolation region includes a nitride-filled trench;and a trench sidewall region disposed between and in contact with eachof the isolation region and the source/drain feature, wherein the trenchsidewall region provides separation between the isolation region and thesource/drain feature, wherein the trench sidewall region includes aspacer layer and a plurality of high-K gate dielectric layer portionsdisposed directly beneath the spacer layer, and wherein thicknesses ofeach of the spacer layer and the plurality of high-K gate dielectriclayer portions along the trench sidewall region are substantiallyuniform.
 19. The semiconductor device of claim 18, wherein the trenchsidewall region further includes a plurality of nanosheet channel layerportions, and a plurality of inner spacer portions, wherein each of theplurality of high-K gate dielectric layer portions is disposed at ananosheet channel layer portion-inner spacer portion interface.
 20. Thesemiconductor device of claim 18, wherein the transistor includes agate-all-around (GAA) transistor.